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aerodynamic resistance
"The bulk meteorologic descriptor of the role of the atmospheric turbulence in the evaporation process" (Oke 1978, p. 107).  It is dependent upon wind speed, surface roughness and atmospheric stability.

albedo
"The ratio of reflected solar radiation to the total incoming solar radiation where both streams are measured across the complete wavelength range of solar radiation (~0.3-4.0 mm)" (Henderson-Sellers and Robinson 1986, p. 423).

anisotropy
The condition of having different physical properties (e.g. KH) in different directions.

aquifer
"A saturated permeable geologic unit that can transmit significant quantities of water under ordinary hydraulic gradients" (Freeze and Cherry 1979, p. 47).

aquitard
"The less-permeable beds in a stratigraphic sequence" (Freeze and Cherry 1979, p. 47).

baseflow
Sustained runoff that is the sum of deep subsurface flow and delayed shallow subsurface flow; however, it is not synonymous with groundwater flow (Ward and Robinson 1990).

Bowen Ratio
The ratio of the sensible and latent fluxes over a surface.

capillary fringe
The area between the vadose and phreatic zones; all pores are filled with water, but the water is held under slight matric tension, such that the addition of a small amount of water will convert this zone to saturated conditions (Gillham 1984).

capillary rise
Movement of water from the saturated zone upward into the unsaturated zone due to surface tension (Dingman 1993).

catchment
"A unit of land on which all the water that falls (or emanates from springs) collects by gravity and fails to evaporate and runs off via a common outlet" (Black 1991, p. 248).

channel precipitation
Direct precipitation onto a water surface.

CC
Clear Cut - A harvesting and regeneration method that removes all trees within a given area. Clear-cutting is most commonly used in pine and hardwood forests, which require full sunlight to regenerate and grow efficiently.

depression storage
The volume of water contained in small surface depressions during or shortly after rainfall or melt, none of which runs off (Horton 1933).

detention storage
Rainwater or snowmelt held in temporary storage on the surface as it moves downslope by overland flow, and which either runs off, is evaporated, or is infiltrated after rainfall or melt ceases (Horton 1933).

dew point
Temperature at which an air parcel becomes saturated if cooled without a change in pressure or moisture content (Henderson-Sellers and Robinson 1986).

emissivity
Degree to which a real body approaches a black body radiator (i.e. a perfect emitter of radiation) (Henderson-Sellers and Robinson 1986).

evaporation
Diffusion of water vapour into the atmosphere from exposed water surfaces.

evapotranspiration
Diffusion of water vapour into the atmosphere from vegetated surfaces.  It represents the combination of evaporation from soil and plant surfaces with plant transpiration (Goudie et al. 1985).

event water
Water that is added to a catchment's surface as rainfall or snowmelt during a storm event.

exfiltration
The removal of water from the soil at the ground surface, together with the associated unsaturated upward flow (Freeze 1974).

falling limb
That portion of the hydrograph where discharge is decreasing with time. Also known as the recession limb.

fractionation
"The separation of a mixture, usually of chemically related or otherwise similar components, into fractions of different properties" (Uvarov et al. 1979, p. 170).

groundwater flow 
That part of streamflow that has infiltrated the ground, has entered the phreatic zone, and has been discharged into a stream channel as spring or seepage water (Chorley 1978).

Horton flow
"Direct surface runoff across saturated soils where rainfall intensity exceeds infiltration plus depression storage" (Chorley 1978, p. 368).

hydraulic conductivity
The constant term in Darcy's Law expressing the ability of a soil or rock to transmit water under a given hydraulic gradient (Chorley 1978).

hydraulic diffusivity
The ratio of the hydraulic conductivity to the volume of water that a unit volume of saturated soil or rock releases from storage per unit decline in hydraulic head.  It is a parameter that combines transmission characteristics and the storage properties (Goudie et al. 1985).

hydraulic gradient
The change in total potential over the change in flow length.

hysteresis
The property whereby a dependent variable exhibits different values according to whether the independent variable is increasing or decreasing (Goudie et al. 1985).

immobile water 
Soil water that remains in place in the soil matrix during infiltration through the vadose zone.

infiltration
Entry of water through the soil surface, via pores or small openings, into the soil mass.

infiltration capacity
The maximum rate at which a given soil can absorb water when it is in a specified condition (Horton 1933).

interception
"The process by which precipitation is trapped on vegetation and other surfaces before reaching the ground" (Goudie et al. 1985, p. 245).

isothermal
At the same temperature throughout. In snowmelt hydrology, this condition implies that the snowpack is at the melting point (273.2K or 0°C) throughout.

isotropy
The condition of having uniform physical properties in all directions.

kriging
A statistical estimation technique used for spatial interpolation and integration.

KETE
Knowledge exchange and technology extension is a program directed by the Sustainable Forest Management Network (SFMN) designed to promote the transfer and implementation of new information and research results to Network partners. 

lag-to-peak
The time difference between the centre of mass of rainfall and the peak discharge rate (Dunne and Leopold 1978).

latent heat
That part of the thermal energy involved in a change of state (e.g. 2.4 MJ kg-1 released when water vapour condenses to liquid) (Goudie et al. 1985).

leaf area index
The proportion of the surface area of one side of all leaves to the plan-view area of the entire plant.

litter
"The surface layer of fallen, dead vegetation lying on the mineral soil" (Chorley 1978, p. 369).

litter flow 
"Downslope flow of water in the litter layer" (Chorley 1978, p. 369).

local evaporation line
The relationship describing parallel variations in 18O and D in water that has undergone evaporation. Water that has undergone evaporation will plot below the mean water line in 18O-D space.

macropore
Large soil pores that may result from biological activity (earthworms, plant root extension and subsequent decay) as well as structural cracks and fissures (Ward and Robinson 1990).

micropore
Small soil pores between individual mineral grains.

mean water line
The relationship describing parallel variations in 18O and D in precipitation: dD = 8d18O + 10 (‰) (Craig 1961).

mixing models
"Models used to explain or predict temporal variations in the solute concentrations of streamflow by taking account of the mixing of water from different sources or the mixing of water within a store" (Goudie et al. 1985, p. 292).

net radiation
"The resultant flux of the solar and terrestrial radiation through a horizontal surface" (Goudie et al. 1985, p. 307).

occult precipitation
Precipitation in liquid (fog drip) and solid (rime) forms that is induced when clouds encounter trees or other vegetation (Dingman 1993).

overland flow
"Water that, failing to infiltrate the surface, travels over the ground surface towards a stream channel either as quasi-laminar sheet flow or, more usually, as flow anastomosing in small trickles and minor rivulets" (Ward and Robinson 1990, p. 220).

partial area runoff
Storm runoff generated by only part of the surface of a catchment (Betson 1964).

PET
Potential Evapotranspiration - the amount of water that could be evaporated and transpired if there was sufficient water available.

phreatic zone
The volume of soil and bedrock below the water table that is saturated (i.e. pores and void spaces are completely filled with water).

pipe flow
Concentrated subsurface flow of water in natural pipes (Jones 1971).

piping
Formation of natural pipes in unconsolidated material by eluviation or other processes of differential subsurface erosion (Jones 1971).

pre-event water
Water that was held in a catchment prior to, and has been discharged into the stream channel during, a storm event.

quickflow
The sum of channel precipitation, surface runoff and rapid subsurface flow, also referred to as direct runoff. Quickflow is the major runoff contribution during storm periods and most floods; however, it is not synonymous with surface runoff (Ward and Robinson 1990).

return flow
Infiltrated water which returns to the surface having flowed for a short distance in the upper soil horizon (Dunne and Black 1970).

rising limb
That portion of the hydrograph where discharge is increasing with time.

saturation overland flow
Surface runoff over saturated soil, the infiltration capacity of which has not been exceeded (Carson and Kirkby 1972).

sensible heat
The addition or subtraction of energy to a body that is sensed as a rise or fall in its temperature (Oke 1978).

SW
Shelterwood Cut - Removing trees on the harvest area in a series of two or more cuttings so new seedlings can grow from the seed of older trees. This method produces an even-aged forest.

SC
Selection Cut -The periodic removal of individual trees or groups of trees to improve or regenerate a stand.

stemflow
That portion of the gross rainfall intercepted by the vegetation canopy which reaches the litter or soil surface by running down stems or trunks (Helvey and Patric 1965).

stomata
"The leaf orifices through which water vapour escapes to the atmosphere" (Ward and Robinson 1990, p. 80).

stomatal resistance
Resistance to diffusion of water vapour through a plant's stomata.

sublimation
"The conversion of a solid direct into vapour, and subsequent condensation, with melting" (Uvarov et al. 1979, p. 409).

subsurface runoff
The sum of shallow and deep subsurface flow, normally equal to the total flow of water arriving at the stream as saturated flow into the stream bed itself and as percolation from seepage faces on the stream bank (Freeze 1972).

subsurface stormflow
That fraction of stormflow generated by lateral subsurface flow of water above water-impeding layers, which reaches the channel without entering the groundwater zone (Whipkey 1967)

surface runoff
That part of total runoff that reaches the catchment outlet via overland and channel flow (Ward and Robinson 1990).

throughfall
That portion of gross rainfall which directly reaches the forest litter through spaces in the canopy and as drip from leaves, twigs and stems (Helvey and Patric 1965).

throughflow
"Water that infiltrates the soil surface and then moves laterally through upper soil horizons towards the stream channels, either as unsaturated flow or, more usually, as shallow perched saturated flow above the main groundwater level" (Ward and Robinson, p. 220).

time of rise
The time difference between the initial rise in streamflow in response to water inputs and the occurrence of peak discharge.

translatory flow
Lateral throughflow of 'old' water stored in the soil and released to channel flow by a process of displacement by 'new' water inputs (Hewlett and Hibbert 1967)

transpiration
Loss of water vapour mainly from leaf cells through pores but also from the leaf cuticle and through lenticels of the stem (Goudie et al. 1985).

vadose zone
The volume of soil and bedrock above the water table that is generally unsaturated (i.e. pores and void spaces are not completely filled with water).

vapour pressure
"The force per unit area created by the motions of the vapour molecules treated in isolation from all other gases in the atmosphere" (Henderson-Sellers and Robinson 1986, p. 430).

variable source areas
Areas contributing to storm runoff.  These can vary in size between storms and during the course of a single storm (Chorley 1978).

wetlands
"Usually flat areas which are covered either periodically, regularly or permanently by shallow water up to a depth of around 6 m.  They include swamps and marshes, bogs, fens, peatlands, seasonally flooded land around lakes and rivers or level, ill-drained plains" (Goudie et al. 1985, p. )

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